More particularly, it relates to a prefilled culture medium bag that can be presterilized and delivered to a laboratory ready for the introduction of a culture containing microorganisms therein.
Microbiologists incubate samples in sterile liquid culture media to detect and perform tests for pathogenic microorganisms. Salmonella, Listeria, Campylobacter and E. coli are some of the typical microorganisms subject to culturing in this manner. Similar kinds of tests are conducted to detect the presence of microorganisms in samples normally expected to be sterile, such as blood, spinal fluid, medical devices, and a wide variety of industrial materials.
Historically, microbiologists prepare sterile liquid culture solutions and buffered diluent solutions (collectively xe2x80x9cculture mediaxe2x80x9d) in glass or plastic bottles (xe2x80x9crigid containersxe2x80x9d). Although rigid containers can be reused, the preparation of culture media in these containers is expensive, labor intensive, and subject to error.
A laboratory that prepares its own culture media typically undertakes a series of steps. First, the container is washed and rinsed to remove any residual substances or chemicals that may inhibit the growth of microorganisms. Then a measured amount of purified water and a powdered culture mix are placed in the container. The water is heated to dissolve the mix in the water and Ph adjustments are made, as necessary. This is followed by sterilizing the container and its contents in an autoclave. The test sample is then introduced into the culture medium after sterilization.
Because the foregoing procedure is labor intensive, many laboratories now prefer to purchase prefilled and presterilized rigid containers, rather than conduct mixing and sterilization themselves. This leaves the laboratory with the task of merely introducing test samples into the containers after they arrive.
Regardless of whether a lab makes and sterilizes its own culture media or purchases prefilled and presterilized containers, rigid containers have been the containers of choice. They can easily withstand the autoclave conditions (121xc2x0 C., 15 p.s.i., 100% steam) necessary to sterilize liquid culture media.
Glass is particularly advantageous as a container because it allows visual inspection of the culture media before and after a sample is added. Because it is a rigid container, it can be easily moved from place to place. It rests easily on any flat surface and does not require supporting racks or similar structures.
In the prefilled situation, the impermeability of glass extends the shelf life of the culture media by preventing evaporative loss. While plastic is used in many instances because it weighs less than glass and is relatively resistant to breakage, many types of plastics cannot withstand autoclave conditions. The types of plastics which can withstand autoclave conditions are expensive, have reduced clarity, and tend to distort or break after repeated autoclave exposure.
In general, rigid containers are expensive to make (the cost of a cap for capped containers can be as much as 25% of the total cost of the container), heavy to ship, subject to breakage, and contribute to total waste disposal. The breakage and weight problems associated with rigid containers are particularly disadvantageous when they are prefilled and presterilized at one geographic location and then shipped to another location for use.
A further problem with rigid containers is that they do not allow a user to easily mix a sample into the culture media. When mixing is required, the container must be shaken to adequately distribute the sample in the media. If shaking will not work because of sample type, the contents of the container must be transferred to a blender bag which is then placed in a machine having reciprocating paddles that pulverize and mix the sample with the culture media. After mixing, the sample and media must be returned to the rigid container for incubation.
As will become apparent, the present invention solves the above problems and provides a more convenient, less expensive, and better way to culture samples.
The invention is a prefilled culture medium bag including a closure means and a gusseted base permitting the bag to stand upright when filled.
The invention incorporates the use of a gusseted plastic bag. For definitional purposes, a gusseted bag is one having a gusseted base which allows the bag to stand alone without any external support. In the preferred embodiment, the gusseted bag is comprised of a pair of thin film plastic sheets that lay one on top of the other when the bag is not filled with a culture medium. The lower portion or region of the sheets are connected together and closed to form the gusseted base. The side edges of the sheets are bonded directly to each other without the use of a gusset. The upper portion or region of the sheets may be spread apart in order to fill the bag.
In accordance with one embodiment of the invention, the liquid culture medium is sterilized before it is placed in a presterilized bag. Presterilization of the liquid culture medium is done by placing the medium in an autoclave and subjecting it to sterilization temperatures and pressures. According to what is presently believed to be the preferred embodiment, the bag is presterilized using a separate procedure of irradiation to kill any microorganisms.
The presterilized bag is then filled with the presterilized culture medium in a clean room. Since the bag is gusseted and self-supporting, it stands up by itself when filled and can be moved from place to place like a rigid container.
The prefilled and presterilized bag is then shipped to a lab for incubating a sample (sometimes called xe2x80x9cculture samplexe2x80x9d). The culture sample is added to the culture medium by opening the bag and subsequently sealing it. Preferably, the bag is designed to have a resealable opening in the form of a xe2x80x9cziplockxe2x80x9d closure, although other ways of sealing the bag may work just as well. After sealing, the sample is incubated in accordance with known incubation procedures, according to sample type.
An alternative method of resealing the bag is to use a closure wire instead of a xe2x80x9czip lockxe2x80x9d closure. The closure wire is connected to the upper portion of one of the sheets, and the closure wire has a length that exceeds the width of the bag. After the culture medium is added to the bag, the upper portions of the pair of sheets, above the wire closure, are bonded together to form an airtight seal. When the bag arrives at the laboratory for use, the upper portion of the bag is spread open to break the airtight seal, allowing a culture sample to be inserted into the bag. Afterwards, to reseal the bag, the upper portion of the bag is folded or rolled about the closure wire, and then the ends of the closure wire are wrapped around the rolled upper portion, to prevent it from unrolling
In an alternative embodiment, the bag and medium are sterilized in the same step by radiation treatment. In this embodiment, a non-sterile culture broth is added to a non-sterile bag and then subjected to radiation treatment by gamma rays or electrons to render the product sterile. This alternative will be further described below.
An advantage of the invention is that it works particularly well in situations where the sample is not easily dissolved in the culture medium. In some cases, in order to obtain a good distribution of the sample, it is necessary to physically stir or beat the mixture. When the above process is used, the solution of medium and sample can be quickly pulverized or kneaded through the walls of the flexible bag, as needed, without transferring bag contents from one container to another. This reduces the risk of introducing unwanted contaminants. As mentioned above, container to container transfer is a drawback in this situation if rigid containers are used.
A second advantage of the invention is that use of a clear, gusseted bag allows visual inspection of the culture medium and sample at any time during the culturing or test process. For example, a user can easily determine whether the contents of a prefilled and sterilized bag have been contaminated at any point in time during shipment or storage. Typically, a prefilled and presterilized bag will be quarantined for a period of time as a manufacturer""s test for sterility prior to supplying it to a laboratory. Quarantine will reveal contamination by visual inspection. If the bag passes quarantine, then it is deliverable to the laboratory as a xe2x80x9cready-to-usexe2x80x9d unit for incubation purposes. Similarly, after the sample is placed in the bag and incubated, the user can visually inspect it for microorganism growth.
A third and most important advantage of the invention is that it significantly reduces laboratory costs. There is now a significant market relating to supplying labs with prefilled and presterilized culture media in ready-to-use, rigid containers. However, there is no mechanism in place for easy recycling of the containers back to the supplier for reuse. Consequently, the containers tend to be used once and then disposed of by the lab. Not only does this create unnecessary work, but the incremental cost of the container alone is significant relative to what is supplied to the laboratory. Replacing rigid containers with gusseted bags or pouches retains all the existing advantages of rigid containers and provides additional advantages relating to significantly lower costs per container (a cost savings of approximately 20-40% per container) and a reduction in total mass and volume of waste material.
Having briefly summarized the invention, it will become better understood after review of the following description, which is to be taken in conjunction with the drawings.